Field of the Invention
The disclosure relates to a process control system and a process control method.
Priority is claimed on Japanese Patent Application No. 2014-061786, filed Mar. 25, 2014, the contents of which are incorporated herein by reference.
Description of Related Art
A process control system is installed in a plant and a factory (hereinafter called simply “plant” as a generic name of them). The process control system controls various types of state quantity (for example, pressure, temperature, flow quantity, and so on). By the process control system, an advanced automatic operation is implemented.
In the process control system, field devices (for example, a measurement device, an operation device, or other devices) are connected to a controller via an I/O module. The controller controls the operation device (for example, an actuator) in accordance with a measurement result of the measurement device (for example, a sensor) so as to control the various types of the state quantity described above.
The field devices are used in the process control system. There are various types of the field devices in accordance with a measurement target and an operation target, and there are various types of input/output signals. For example, there are an analog signal of “4 to 20 [mA]”, a digital signal of “24 [V]”, a contact signal, a thermocouple signal, and so on. For the reason, the field device is connected to the controller via the I/O module which converts a signal, which is received from the field device, to a signal which can be processed by the controller.
Examples of a process control system installed in a plant are disclosed in Japanese Unexamined Patent Application Publication No. 2007-286705, Japanese Unexamined Patent Application Publication No. H8-179816, Japanese Unexamined Patent Application Publication No. H7-135510, Japanese Unexamined Patent Application Publication No. 2001-514406, and Japanese Patent No. 4860620. For example, in Japanese Unexamined Patent Application Publication No. 2007-286705, a process control system which suppresses a virtual memory mistake so as to improve a performance of a controller included in the process control system is disclosed. The virtual memory mistake is called as page fault, and the virtual memory mistake occurs in a case of using the virtual memory.
Communications performed by the process control system include a control data communication and a device data communication. The control data communication is a communication of transmitting and receiving data for a process control, and the device data communication is a communication of transmitting and receiving data which indicates a normality of the field device.
The control data communication is a periodic communication performed between the controller and the field device. In the control data communication, because there is a need to control a process data in real time, a priority of the control data communication is set to be higher than that of the device data communication. On the other hand, the device data communication is performed between a device manager and the field device via the controller. The device manager is a device for receiving a normality of the process control system. In contrast to the control data communication, because there is no need for the device data communication to communicate in real time, the priority of the device data communication is set to be lower than that of the control data communication so as not to affect the control data communication.
Both the control data communication and the device data communication are implemented by communicating between the controller and the I/O module by a command response method. Specifically, in the control data communication, the controller transmits a command for requesting data (for example, measurement data of a sensor) to the I/O module, and the I/O module transmits the data requested by the command to the controller. Similarly, in the device data communication, the controller transmits a command for requesting data (for example, data indicating the normality of the field device) to the I/O module, and the I/O module transmits the data requested by the command to the controller.
Recent field devices become intelligent, for example, most of the recent field devices have a self-diagnosis function for diagnosing states of a self-device. So as to collect various types of data transmitted from the field devices having the function in real time, there is a need to shorten a cycle of the communication of the command response method so as not to affect the control data communication. For the reason, there is a problem that a communication load and a load of the controller are increased. So as to resolve the problem, in a case of using a high-speed communication network and a high-performance controller and I/O module of which processing ability is high, costs are greatly increased.
The field devices having the self-diagnosis function include a field device which can autonomously notify a higher-level device of data which indicates a self-diagnosis result, and an abnormality and a variation which are generated in the self-device. Because the field device autonomously transmits the data to the controller via the I/O module, the communication of the command response method can be omitted and the load of the controller can be reduced.
Because the conventional I/O module has only a slave function of a master-slave communication, there is a need for the I/O module to also have the function of autonomously transmitting data so as to efficiently notify the controller of the data which is autonomously transmitted from the field device. However, because the autonomous notification is a non-periodic interrupt processing for the controller, there is a possibility of increasing the load of the controller and affecting the control data communication.
Further, in the process control system, there is a case that a plurality of controllers needs data from a particular I/O module. For example, there is a case that measurement data, which is output from the particular I/O module and used by a controller which controls an upstream process, is to be also used by another controller which controls a downstream process. In this case, there is a need to transmit the data from the particular I/O module to the plurality of controllers. However, the real-time processing cannot be performed (the process control is delayed and not performed in real time), and the load of the communication between the controller and the I/O module is increased.